Simulated emerald gemstone

ABSTRACT

A SIMULATED EMERALD GEMSTONEOF THE SINLE CRYSTAL GARNET STRUCTURE IS GROWN BY THE CZOCHRALSKI TECHNIQUE IN THE FORM OF Y3AL5O12, KNOWN AS YTTRIUM-ALUMINUM GARNET (YAG) AND IS DOPED WITH SMALL AMOUNTS OF METAL OXIDES INCLUDING CHROMIUM OXIDE, COBALT OXIDE, IRON OXIDE, NEODYMIUM OXIDE TO FORM A CRYSTAL HAVING A DEEP GREEN COLOR WITH A SLIGHT BLUISH SHADE AND EMERALD-LIKE FLAWS THEREIN.

United States Patent 3,761,292 SIMULATED EMERALD GEMSTONE Donald A. Lepore, Florham Park, Richard C. Puttbach,

Parsippany, and Richard J. De Stefano, Roselle Park,

NJ., assignors to Litton Systems, Inc., Beverly Hills,

Calif.

No Drawing. Filed Sept. 13, 1971, Ser. No. 180,176

Int. Cl. C04b 35/00 US. Cl. 106-42 2 Claims ABSTRACT OF THE DISCLOSURE A simulated emerald gemstone of the single crystal garnet structure is grown by the Czochralski technique in the form of Y Al O known as yttrium-aluminum garnet (YAG) and is doped with small amounts of metal oxides including chromium oxide, cobalt oxide, iron oxide, neodymium oxide to form a crystal having a deep green color with a slight bluish shade and emerald-like flaws therein.

BACKGROUND OF THE INVENTION The present invention relates to simulated gemstones and, more particularly, to a simulated emerald gemstone made from doped yttrium-aluminum garnet.

Yttrium-aluminum garnet (YAG) was first grown by the Bell Telephone Laboratories in 1964. Prior to that time, James W. Nielsen described garnet type gemstones in his Patent No. 3,091,540 which issued on May 28, 1963 from an original filing date of Aug. 25, 1959, and which he assigned to the Bell Telephone Laboratories. In the Nielsen patent, garnet gemstones of the yttrium-gallium garnet structure (Y Ga O and additives of various types which are capable of coloring the garnet gemstones are described.

SUMMARY OF THE INVENTION The utilization of the method and procedure outlined in the Nielsen patent produced gemstones of limited size. Further, the combinations of additives taught by Nielsen do not produce the relatively deep green color with a slight bluish shade which is most acceptable as a color for a simulated emerald gemstone. Most emeralds found in nature come in various shades of green and include flaws in random patterns. That is, a natural emerald is not a perfect crystalline structure but has random discontinuities which appear as cracks or flaws across the surface of the stone.

Accordingly, it is an object of the present invention to provide a large unicrystalline gemstone of the garnet structure which may be utilized as a simulated emerald.

Another object of this invention is to provide a simulated emerald having a deep green color with a slight bluish shade, and further to provide a simulated emerald of unicrystalline garnet structure that has a deep green color with bluish overtones which is flawed in the random pattern of a natural emerald.

In accomplishing these and other objects, there is provided a single crystal gemstone of the garnet structure which is grown from a melt consisting of aluminum oxide and yttrium oxide into which substituents of metal oxides including chromium oxide, cobalt oxide, iron oxide, neodymium oxide and others are added in small quantities. A boule grown from the melt by the Czochralski crystal growing process is then cut and polished into simulated emerald gemstones.

BRIEF DESCRIPTION OF THE INVENTION Through the utilization of the Czochralski process, a mixture of yttrium oxide and aluminum oxide is carefully weighed in a 3:5 molar ratio and placed within an iridium crucible. The crucible is heated to between 1800 and 2100 C. for 5 to 10 hours to produce a melt. A sapphire rod with a seed crystal of yttrium-aluminum garnet at the tip thereof is then introduced into the melt. The seed is rotated and slowly withdrawn from the melt thus allowing the molten material to crystallize thereon in the form of a boule. A typical rotation speed may vary between the rates of 5 to 50 r.p.m. with the withdraw rate varying between 0.01 to 0.40 inch per hour. The single crystal aluminum yttrium garnet resulting therefrom is a durable crystalline material having a hardness between 8% and 8 /2 on the Mohs scale. The refractive index of the yttrium-aluminum garnet crystal thus formed is 1.833.

The yttrium-aluminum garnet crystal, Y Al O may be doped or colored by substituting within the basic formula as follows: Y M Al R O The substituents for M and R are: (M) Ce, Nd, Sm, Gd, Dy, Ho, Er, Tb, Yb, Lu, Eu, Tm; and (R) Co, Fe, Ga, Cr, V, Mn.

The boule withdrawn from the melt in the manner thus described may typically be formed in 12-inch lengths with a diameter varying between 1.5 to 2.5 inches. The normally clear color of the YAG may be varied by the addition or substitution of the elements indicated above. Further, it has been found that the addition of some of these elements aids the forming of flaws throughout the yttrium-aluminum garnet boule.

The following examples are given by way of illustration.

EXAMPLE I A mixture consisting of 3 parts yttrium oxide to 5 parts aluminum oxide, weighed in a molar ratio, was mixed within an iridium crucible with the substitution of dopants for an equal amount by weght of aluminum oxide in the following range: 0.11% to 0.27% by weight of chromium oxide; 0.21% to 1.38% by weight of cobalt oxide; and 0.20% to 1.33% by weight of iron oxide. The contents of the iridium crucible were then heated to a temperature of 1800 to 2100 C. and a seed of yttrium-aluminum garnet introduced into the melt. It should be noted that the seed was not doped. The seed was then withdrawn from the melt at a rate of .03 to to .10 inch per hour while being rotated at approximately 5 to 20 rpm. The resulting single crystal boule of yttrium-aluminum garnet has a deep green color.

EXAMPLE II The procedure in Example I was followed with the exception that the yttrium oxide made up 56.69% of the total weight of the melt while the aluminum oxide made up 41.55% by weight. The chromium oxide made up 0.13% by weight with the cobalt oxide making up 0.83% and iron oxide making up 0.80% thereof by weight. The chromium, cobalt and iron oxides are substituted for an equal amount by weight of aluminum oxide in accordance with the formula set forth hereinabove, i.e., Y Al Cr CO Fe O In the example, the yttrium oxide and the aluminum oxide were weighed to within 0.1% of the value indicated; while the other oxides were weighed to within 0.02% of the value indicated. The seed was then introduced into the melt whose temperature was 1950 C. and withdrawn at a rate of 0.1 inch per hour while rotated at 8 rpm.

EXAMPLE III formed had yellowish tints in combination with the deep green color.

3 EXAMPLE iv The procedure set out in Example II was repeated with the exception that 1.5% of cerium oxide and 3.8% of erbium oxide by weight were substituted in the melt in place of an equal amount of yttrium oxide. The single crystal boule thus formed had a deep green color with a yellowish tint and orange overtones.

EXAMPLE V The process of Example I was repeated substituting a small amount of neodymium oxide for the yttrium oxide. It has been found that the neodymium oxide does not fit well into the yttrium-aluminum garnet lattice thus causing flaws formed by bubbles arranged in a veil-like pattern. These flaws were randomly arranged and demonstrated reproducibility between single crystal boules of various melts. In the process, the substituted amount of neodymium oxide may be varied between 0.05 to 0.30%. The resultant unicrystalline yttrium-aluminum garnet boule had a relatively deep green color with a slight bluish shade and randomly arranged flaws.

EXAMPLE VI The procedure of Example II was repeated with the exception that 0.14% by weight of neodymium oxide was substituted in the melt in place of an equal amount of yttrium oxide in accordance with the formula set forth hereinabove, i.e., Y Nd A1 -;Cr C0 Fe O The gemstone crystals thus produced were characterized by a deep green color with a slight bluish shade having randomly arranged flaws throughout.

It will be understood that the examples set forth above are intended merely as illustrative of the advantages of the present invention gained through the doping of yttrium-aluminum garnet with oxides of chromium, cobalt, iron, neodymium, cerium, samarium, erbium or other substituents. The unique color formed by the combination of these oxides and the flaws formed by the addition of the neodymium oxide produces a flawed, simulated emerald having a deep green color with a slight bluish shade that is unknown to those skilled in the art. Obviously, the flaws introduced by the neodymium oxide may be introduced into other single crystals of various colors than those set out by way of example hereinabove.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A single crystal simulated emerald of the garnet structure having a deep green color and random veil-like flaws pulled from a melt composition represented by the formula Y M Al R O in which M is Nd and R is Cr-i-Co-I-Fe, all present in the melt in the following weight percent range:

Percent Cr O 0.11-0.27 C0 0 0.21-1.38 Fe O 0.20-1.33 Nd O 0.05-0.30

said crystal being formed on a seed of yttrium aluminum garnet pulled from the melt at a rate of .03 to .10 inch per hour while being rotated at about 5 to 20 r.p.m.

2. A single crystal simulated emerald as claimed in claim 1 wherein said melt is represented by the formula Y2 995Nd 5Al4 7cr g CO 5Fe o5O1 and consists essentially of 56.55% Y O and 41.55% A1 0 by weight plus 0.13% Cr O 0.83% C0 0 0.80% Fe O and 0.14% Nd O by weight.

References Cited UNITED STATES PATENTS 3,252,103 5/1966 Geusic et a1 330-5 3,632,521 1/1972 Holloway et al 252--30l.4 3,595,803 7/1971 Dugger 252-301.4 3,091,540 5/1963 Nielsen 10642 3,614,662 10/1971 Monchamp 252-301.4 3,663,474 5/1972 Lee et al 252-3014 3,533,956 10/1970 Snitzer 252301.4 3,591,517 "7/1971 Van der Ziez et al. 330-4.3

FOREIGN PATENTS 1,429,754 1/1966 France 3305 1,391,101 1/1965 France 3305 1,055,099 1/1967 Great Britain.

OTHER REFERENCES Vanuitert, L. G. et al.: Growth of Large Yttrium Aluminum Garnets,, in Tourn. Amer. cer. soc., 48 (2), 1965 pp. -8 (TP785A62).

Hammer: Growth of Single Crystals of Yttrium Aluminum Garnet Doped with Nd+++ and Cr+++ by Flame Fusion Process for Solid State Lasers, Chem. Abstracts, vol. 71 (1969), p. 333, item 7266r.

Bass et al.: Color Centers in Yttrium Gallium Garnet and Yttrium Aluminum Garnet, Chem. Abstracts, vol. 67 (1967), p. 11416, item 120995h.

Arsenener: Defects in Garnet Single Crystals Grown by Zone Chem. Abstracts, vol. 69 (1968), p. 8500, item 90745y.

Kiss et al.: Cross-Pumped Cr+ -Nd+ Yag Laser System, Applied Physics Letters, Nov. 15, 1964, vol. 5, No. 10, pp. 200-202.

HELEN M. MCCARTHY, Primary Examiner US. Cl. X.R. 23273 SP, 301 SP 

